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13 old > Turning points - Wave particle duality > Flashcards

Turning points - Wave particle duality Flashcards

1
Q

TP Chapter 2 Q) Describe Newton’s corpuscular theory of light

A

A) That light is made of corpsucles. Different colours are made of diffent size corpuscles.

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2
Q

TP Chapter 2 Q) Describe Huygens’ theory of light

A

A) That light is made of waves. Wave behaviour can be described by drwaing geometrical wavefronts.

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3
Q

TP Chapter 2 Q) What would happen in refraction according to Newton?

A

A) Light would slow down when it enter’s a material from air. This causes the change in direction in the material and due to light speeding up when it reenters air, explains it’s change in direction when light emerges.

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4
Q

TP Chapter 2 Q) What would happen in refraction according to Huygen?

A

A) Light would speed up due to an unknown short range attractive force between the material and the corpuscle. This would increase the ‘vertical’ component of velocity but not horzontal - changing the directino of light. When light emerges the same force ‘attracts’ the light back - reducing the ‘vertical’ component of velocity.

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5
Q

TP Chapter 2 Q) State three reasons why Huygen’s theory was not accepted

A

A) Newton’s other theories were successful. Huygen’s theory was based on longitudinal waves which could not explain polarisation. Huygen’s theory could not explain sharp shadows.

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6
Q

TP Chapter 2 Q) Outline Young’s double slit experiment

A

A) Light is shone through a single slit which the is shone through two narrow slits. Light then travels onto a screen to display an interference pattern.

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7
Q

TP Chapter 2 Q) State the equation for Young’s double slit

A

A) w = λD/s

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8
Q

TP Chapter 2 Q) What did Huygens’ theory predict for Young’s double slit experiment

A

A) That an intereference pattern would occur with bright and dark fringes.

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9
Q

TP Chapter 2 Q) What did Newton’s theory predict for Young’s double slit experiment

A

A) That there would be two columns of light where the corpuscules went through the slits.

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10
Q

TP Chapter 2 Q) What does Young’s double slit tell you about the nature of light?

A

A) That light is a wave.

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11
Q

TP Chapter 2 Q) Explain why more than two bright fringes are seen in Young’s double slit experiment

A

A) Bright fringes are caused by constructive intereference. This occurs when there is a phase difference of 0, 360, 720 etc degrees. This is caused when there is a path difference of 0,1,2 etc wavelengths. This occurs due to the geometry of the slits and screen.

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12
Q

TP Chapter 2 Q) How did Fizeau measure the speed of light?

A

A) As constructive interference occurs when there is a path difference of an integer number of wavelengths. As the wavelength of ight is small it is highly likely that many fringes would occur on a screen.

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13
Q

TP Chapter 2 Q) Explain what was happening when Fizeau did not see light

A

A) Light shone through a gap, but by the time light had travelled and reflected back, the wheel had turned from a gap to a tooth. The light was blocked out by the tooth in the cog.

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14
Q

TP Chapter 2 Q) Explain what was happening when Fizeau did see light

A

A) The wheel had turned to the next gap by the time light had travelled to the mirror and reflected.

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15
Q

TP Chapter 2 Q) State the equation for Fizeau’s experiment

A

A) c = 4dnf

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16
Q

TP Chapter 2 Q) Why was Fizeau’s measurement of the speed of light in water significant?

A

A) Newton predicted light travelled faster in water, where as Huygen predicted light travelled slower in water than air. It was shown the the speed of light in water was infact slower than in air.

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17
Q

TP Chapter 2 Q) What did Maxwell predict?

A

A) Light was made of transverse electromagnetic waves. He predicted the speed of all the waves and predicted there would be a spectrum of electromagnetic waves.

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18
Q

TP Chapter 2 Q) What two components make up EM waves and what is the phase difference between them?

A

A) Electric and magnetic waves have a phase difference of zero.

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19
Q

TP Chapter 2 Q) How was Maxwell’s waves different than Huygens?

A

A) They were transverse instead of longitudinal.

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20
Q

TP Chapter 2 Q) How did Maxwell predict the speed of light?

A

A) c = 1/√μ0ε0

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21
Q

TP Chapter 2 Q) Who tested Maxwell’s predictions?

A

A) Hertz

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22
Q

TP Chapter 2 Q) How did Hertz detect radio waves?

A

A) Using a metal loop.

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23
Q

TP Chapter 2 Q) How did Hertz measure the speed of light using stationary waves?

A

A) Use c = f x λ, where wavelength is the distance between two antinodes.

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24
Q

TP Chapter 2 Q) How did Hertz show the transverse nature of the electromagnetic waves?

A

A) By showing the waves can be polarised.

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25
Q

TP Chapter 2 Q) How did Hertz show the magnetic nature of radio waves

A

A) Changing magnetic flux casued by the radiowave (created by a dipole) induced an EMF in a metal loop.

26
Q

TP Chapter 2 Q) How did Hertz show the electric nature of radio waves

A

A) A second dipole aligned with the first would detect a changing electric field.

27
Q

TP Chapter 2 Q) Why does the EMF drop to zero when the loop is rotated 90 degrees

A

A) Due to the dipole, the EM wave is polarised. If the loop is rotated 90 degrees there is now no change in magnetic flux to cause an EMF.

28
Q

TP Chapter 2 Q) What is a blackbody?

A

A) An object that absorbs and emits all wavelengths

29
Q

TP Chapter 2 Q) What is the ultraviolet catastrophe?

A

A) That with the classical interpration of light, it’s intensity should tend to infinity near the ultraviolet wavelengths. This would violate the principle of energy conservation.

30
Q

TP Chapter 2 Q) Who resolved the ultraviolet catastrophe?

A

A) Planck. By quantising light due to quantising electron oscillations.

31
Q

TP Chapter 2 Q) What is the photoelectric effect?

A

A) The phenomena of electrons being liberated from a metal surface by incident electromagnetic waves above the threshold frequency.

32
Q

TP Chapter 2 Q) What would the particle nature of light predict for the photoelectric effect?

A

A) That there would be a threshold frequency, below which light would not cause the photo electric effect. Increasing intensity of light would increase the number of photoelectrons emitted per second.

33
Q

TP Chapter 2 Q) What would the waves nature of light predict for the photoelectric effect?

A

A) That any frequency would cause the photoelectric effect but it would cause a delayed emission if it is below the threshold frequency. Increasing the intensity of light would not change the number of photoelectrons per second but would increase the kinetic energy per photon.

34
Q

TP Chapter 2 Q) How do we measure the maximum kinetic energy of a photoelectron?

A

A) By multiplying the stopping potential by the charge of the electron.

35
Q

TP Chapter 2 Q) Draw a graph to show how we measure the work function and Plank’s constant

A

A) y - axis = KE max x -axis = frequency. Expect a linear graph with a negative intercept if extrapolated.

36
Q

TP Chapter 2 Q) What would the intensity of the incident light affect?

A

A) It woud increase the number of photoelectrons but it would not increase their maximum kinetic energy.

37
Q

TP Chapter 2 Q) What is the De Broglie hypothesis?

A

A) Particles have wave like properties. λ = h / p

38
Q

TP Chapter 2 Q) What is the De Broglie equation?

A

A) λ = h/p = h/mv

39
Q

TP Chapter 2 Q) Electrons can be diffracted - what does this imply about their nature?

A

A) Electrons can behave as waves

40
Q

TP Chapter 2 Q) Explain why an electron with the same De Broglie wavelength as a neutron have more kinetic energy?

A

A) As if they have the same momentum, due to the lower mass the electron would have a higher velocity. As KE is proportional the v2 the electron has a higher kinetic energy.

41
Q

TP Chapter 2 Q) What happens to the ring when you accelerate the electrons faster?

A

A) The rings become narrower as the debroglie wavelength has decreased.

42
Q

TP Chapter 2 Q) State a formula that links the De Broglie wavelength to the anode voltage

A

A) λ = h/√2emVA

43
Q

TP Chapter 2 Q) State evidence for the wave and particle nature of electrons and light

A

A) Electrons: wave - electron diffraction, particle - emission of light of flourescent tube. Light: wave - Young’s double slit, particle - photoelectric effect.

44
Q

TP Chapter 2 Q) State the two types of electron microscopes

A

A) STM and TEM

45
Q

TP Chapter 2 Q) What does TEM stand for?

A

A) Transmission Electron Microscopy

46
Q

TP Chapter 2 Q) How are electrons emitted in a TEM?

A

A) Thermionic emission

47
Q

TP Chapter 2 Q) What does TEM imply about the nature of light?

A

A) Electron behave as waves as they diffract (show interference).

48
Q

TP Chapter 2 Q) What is the typical size of an atom?

A

A) 10-10 m

49
Q

TP Chapter 2 Q) Why do electron need to be accelerated in a TEM?

A

A) To increase the electrons velocity which decreases the debroglie wavelength. This increases the resolution of the TEM.

50
Q

TP Chapter 2 Q) How are the electrons turned into an image at the end of a TEM?

A

A) Electrons emit light on a flourescent screen.

51
Q

TP Chapter 2 Q) What does the condenser lens do?

A

A) The condensor lens deflects the electrons into a wide parallel beam incident uniformly on the sample.

52
Q

TP Chapter 2 Q) What does the objective lens do?

A

A) The objective lens then form an image on the sample.

53
Q

TP Chapter 2 Q) What does the magnifier lens do?

A

A) The projector lens then casts a second image onto the flourescent screen.

54
Q

TP Chapter 2 Q) Explain how sample thickness affects the image quality

A

A) Increasing the sample thickness reduces the speed of the electrons. This causes the debroglie wavelength to be larger and leads to a worse resolution.

55
Q

TP Chapter 2 Q) Explain how lens aberration affects the image quality

A

A) Lens abberation is where the electrons are travelling at different speeds and therefore are deflected by different amounts by the magnetic fields. This causes the different speed electrons to focus at different points leading to a blurry image.

56
Q

TP Chapter 2 Q) Explain how magnetic lenses work

A

A) They deflect the electron using a magnetic field. This is similar to how light is refracted through a lens to focus light.

57
Q

TP Chapter 2 Q) Explain why magnetic lens deflect electrons without changing their kinetic energy

A

A) Magnetic force on a moving electron is always perpendicular to its velocit. So no work is done on the electron by the field as the electron is not accelerated in the direction of motion.

58
Q

TP Chapter 2 Q) What does STM stand for?

A

A) Scanning Tunneling Microscope

59
Q

TP Chapter 2 Q) What is quantum tunnelling?

A

A) Due to the wavelike nature of particles, there is a finite probability they can ‘tunnel’ through a barrier even though the particle does not have the required energy.

60
Q

TP Chapter 2 Q) What are the two modes for a STM?

A

A) Fixed height or fixed current

61
Q

TP Chapter 2 Q) Why does there need to be a potential difference applied to the surface of the material and the tip of the scanner?

A

A) So that the current only flows one way (from - to +).

62
Q

TP Chapter 2 Q) Why does the gap between the tip of probe and surface need to be narrow?

A

A) The smaller the gap, the greater the chance that tunelling occurs.

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